Two-stage hydrogenation process for producing oxidation resistant lubricants



United States Patent TWO-STAGE HYDROGENATION PROCESS FOR lliQjDgClNG OXIDATION RESISTANT LUBRI- James Van Dyck Fear, Media, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application January 13, 1958 Serial No. 708,346

2 Claims. (Cl. 208--57) This invention relates to producing oxidation resistant lubricants by a plural stage hydrogenation process.

It is known in the art to improve by hydrogenation processes the antioxidant additive response of petroleum lubricating oils, as indicated by the oxidation resistant characteristics of the lubricating oil containing an antioxidant additive. The mechanism of the improvement has not been fully understood, and consequently the manner of hydrogenation which has been employed previously has not been adapted to produce oxidation resistance good enough to meet requirements in some uses of petroleum lubricating oils. The process of the present invention provides a novel manner of hydrogenation, based in part upon recognition of important factors involved in the mechanism of improvement of additive response by hydrogenation.

It has been found that when petroleum lubricating oil is hydrogenated under certain conditions involving the use of temperatures within the approximate range from 650 to 850 F., a remarkable improvement is obtained in additive response. The improvement is believed to be attributable to the fact that some polycyclic naphthene hydrocarbons are converted into compounds having one less naphtheue ring as a result of destruction of one of the rings in the molecule.

One ditficulty presented in taking advantage of this effect results from the fact that the aromatic hydrocarbons in petroleum lubricating oils tend to decompose and form undesirable products such as coke, when subjected to the hydrogenationconditions which provide the beneficial conversion of polycyclic naphthenes. The present invention provides a manner of overcoming this difficulty by subjecting petroleum lubricating oil to hydrogenation under different conditions prior to the hydrogenation designed to open naphthene rings in polycyclic naphthenes. The previous hydrogenation, hereinafter referred to as the first stage hydrogenation, serves to convert aromatic rings in some of the lubricatingoil constituents into naphthene rings. This reduction in aromaticity of the lubricating oil results in a reduction in the undesirable reaction products produced in the subsequent hydrogenation, hereinafter referred to as the second stage hydrogenation.

During the second stage hydrogenation, the naphthene rings which are opened as a result of the hydrogenation include those which existed in the original lubricating oil and also some of those which were formed in the preceding hydrogenation. The result of these conversions is a lubricating oil product which has highly satisfactory oxidation resistance when inhibited by means of known antioxidant additives such as alkylated phenols.

It is frequently advantageous to follow the second stage hydrogenation by a further treatment in which undesirable decomposition products produced in small amount during the hydrogenation are removed or converted. A relatively mild hydrogenation or other suitable finishing treatment can be employed to bring about this result. The mild hydrogenation however gives generally superior results to other methods,.and is therefore preferred.

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The charge oil which is subjected to the hydrogenation according to the invention is a petroleum lubricating oil having Saybolt Universal viscosity at 100 F. of at least 50 seconds and more preferably at least 100 seconds. Usually the lubricating oil will not have a viscosity of more than about 300 Saybolt Universal seconds at 210 F. Preferably not more than 5 volume percent of the charge oil has boiling point below 600 F.

The first stage hydrogenation is performed at a temperature in the approximate range from 450 to 750 F. Preferably the pressure is within the approximate range from 150 to 3000 p.s.i.g. A preferred manner of opera tion involves percolating the charge oil in liquid phase through a bed of solid hydrogenation catalyst particles having size within the approximate range from 4 to 30 mesh. The liquid hourly space velocity in such percola tion is preferably within the approximate range from 0.5 to 10 volumes of charge per volume of catalyst bed per hour. The hydrogen consumption is preferably within the approximately range from 25 to 500 standard cubic feet of hydrogen per barrel of charge.

The first stage hydrogenation is necessary in order to convert aromatic compounds, which would otherwise form undesirable products in the following hydrogenation, into compounds which do not form undesirable products in the following hydrogenation. The conversion products produced in the first stage hydrogenation are in some instances compounds which areconverted during the following hydrogenation into products having high oxidation stability.

The second stage hydrogenation is performed at a temperature Within the approximate range from 650 to 850 F. Preferably the pressure is within the approximate range from 100 to 2500 p.s.i.g. The preferred contacting procedure is similar to that previously described with reference to the first stage hydrogenation. The space rate is preferably within the approximate range from 0.25 to 5. The hydrogen consumption'is' preferably within the approximate range from 25 to 500 standard cubic feet of hydrogen perbarrel of charge.

The second stage hydrogenation brings about an advantageous opening of naphthene rings in polycyclic naphthene compounds, and thereby produces an oil prodnot which when inhibited by known antioxidant additives is highly resistant to'oxidatiorn In cases where a mild hydrogenation is employed following the second stage hydrogenation, the conditions employed in such mild hydrogenation preferably include temperature within the approximate range from 600 to 650 F., pressure within the approximate range from 100 to 1500 p.s.i.g., and liquid hourly space velocity Within the approximate range from 0.5 to 5 volumes of oil per volume of catalyst bed per hour. The hydrogen consumption is usually within the approximate range from 5 to 50 standard cubic feet per barrel of oil.

Any suitable known metallic hydrogenation catalyst can be employed in each of the hydrogenations involved 7 in the process according to the invention. Such catalysts include those comprising the metals, cobalt, molybdenum, platinum, nickel, iron, etc. or oxides or sulfides of such metals. Preferably the metallic catalyst is associated with a suitable known carrier such asbauxite; alumina, silica gel, silica-alumina composites, etc. A preferred catalyst for use in each of the hydrogenation stagesis one comprising cobalt molybdate.

The first stage hydrogenation is performed under conditions .which inhibit conversion of aromatic compounds to carbonaceous deposits. Factors contributing to this inhibition include relatively low temperature, relatively high hydrogen pressure and relatively high space rate. The second stage hydrogenation, on the other hand, is performed under conditions of greater severity, in the sense of conditions which would tend to produce excessive conversion of aromatic compounds to carbonaceous deposits if applied to the charge stock directly, i.e. without the intervening first stage hydrogenation.

In one embodiment, the product of the first stage hydrogenation is heated, by indirect heat exchange, prior to introduction into the second stage. In this embodiment, the heating preferably raises the temperature of the first stage product at least 25 F.

In other embodiments, where such heating is not performed, other measures are taken to provide greater severity in the second stage hydrogenation. In one embodiment, the pressure is reduced from that prevailing at the first stage outlet, by afiirmative release of pressure, to provide a pressure in the second stage which is lower than that which would prevail in view of the pressure in the first stage and the normal pressure drops in the equipment. 'In this embodiment, the difference in average pressure in the two zones is preferably at least 500 psi.

The entire effiuent from the first hydrogenation stage is in one embodiment introduced into the second hydrogenation stage. In another embodiment, gaseous mate rials are separated from the oil product of the first stage, and preferably recycled to the first stage. Such separation can be performed at the pressure prevailing at the first stage outlet, or after reduction of pressure. The liquid products, after separation of gaseous material, are introduced into the second stage. It is usually desirable to introduce additional hydrogen into the second stage.

The respective stages are preferably performed in separate vessels, in order to facilitate operations, such as heating or release of pressure, designed to increase the severity of the second stage. However, it is within the scope of the invention to perform the stages in a single vessel, afiirmative internal means for increasing the severity being provided between the stages.

Gaseous materials are separated in conventional manner from the liquid products of the second stage hydrogenation. These gases, which usually contain hydrogen, can be recycled to the first stage hydrogenation, the second stage hydrogenation, or partly to each.

The process according to the invention provides a product which is particularly susceptible to improvement by known antioxidant additives generally. Examples of suitable additives which are advantageously added to the product are the alkylated phenol oxidation inhibitors, which are well known as a class in the prior art, e.g. the polyalkyl aryl hydroxy compounds such as 2,6-ditertiary butyl-4-methyl phenol, 2,4-dimethyl-6-tertiary octyl. phenol, pentamethyl phenol, pentaethyl phenol, tritertiary butyl phenol, 2-isopropyl-4,6-dimethyl phenol, Z-tertiary butyl-4,6-dimethyl phenol, Ztertiary amyl-4,6-dimethyl phenol, 4-rnethyl-2,6-diisopropyl phenol, -2.6-ditertiary amyl phenol-4-tertiary butyl phenol, 2,4,6-triisopropyl phenol, etc. Other known types of oxidation inhibitors can also be employed, for example various compounds of sulfur or phosphorus or of sulfur and phosphorus, various amines, etc. Examples of such oxidation inhibitors are sulfurized lauryl oleate, sulfurized terpenes, alkyl sulfides, tributyl phosphite, lecithin, diphenyl amine, etc.

The following example illustrates the invention:

A furfural-refined and dewaxed, lubricating oil distillate from parafiinic-naphthenic crude is employed as the charge stock. The boiling range of the dewaxed oil is within the approximate range from 600 to 820 F. The viscosity of the distillate at 100 F. is 100 Saybolt Universal seconds and at 210 F. is 39 Saybolt Universal seconds. The A.P.I. gravity is 33, the sulfur content 0.1 weight percent and the aromatic hydrocarbon content about 12 Weight percent. The first hydrogenation stage is performed in the presence of a solid granular catalyst comprising about 12.5% cobalt molybdate on a bauxite base. This is a well known hydrogenation catalyst. The conditions employed in the first stage are the following:

600 F., 1500 p.s.i.g. and liquid hourly space velocity of one. The hydrogenation results in a product having considerably fewer aromatic rings than the charge stock. The second stage is performed in the presence of a solid granular catalyst comprising about 12.5% cobalt molybdate on an alumina base. The conditions are the following: 675 F., 500 p.s.i.g. and liquid hourly space velocity of one.

The oxidation stabilities of the products of the first and second stages (containing 0.4% of 2,6-ditertiary butyl p-cresol) are determined by an oxidation test wherein 13 ml. of sample are placed in a Sligh oxidation tube with five two-inch lengths of copper wire. The tube is flushed with oxygen and heated in a bath at C. The time which elapses before the pressure in the tube decreases 60 of Hg as a result of oxygen takeup by the oil is recorded as the measure of resistance to oxidation. Each of the hydrogenations increases the stability as determined by this test. The product of the second stage hydrogenation can be further improved, if necessary, with respect to antioxidant additive response by subjection to a relatively mild hydrogenation at 600 F. and 500 p.s.i.g. and liquid hourly space velocity of one, employing the same catalyst as in the second stage.

The rate of formation of solid carbonaceous reaction products in the second stage hydrogenation is considerably less as a result of the first stage hydrogenation than in a process where the charge oil is directly subjected to the conditions employed in the second stage hydrogenation. The product obtained in the second stage hydrogenation is also beneficially different from that which would be obtained in the absence of the first stage hydrogenation, in that there is some opening during the second stage hydrogenation of naphthene rings which were formed in the first stage hydrogenation by saturation of aromatic rings.

Generally similar results to those described above are obtained in a plural stage hydrogenation according to the invention of lubricating oils derived from paraffinic and naphthenic base crudes. Generally similar results are also obtained employing other hydrogenation catalysts such as those previously mentioned either with the same or different catalysts in the respective stages.

The invention claimed is:

1. Process for producing stable petroleum lubricating oil which comprises: contacting petroleum lubricating oil with hydrogen and a metallic hydrogenation catalyst at a temperature within the approximate range from 450 to 750 F., pressure within the approximate range from 150 to 3000 p.s.i.g., and liquid hourly space velocity within the approximate range from 0.5 to 10; and subsequently contacting said oil with hydrogen and a metallic hydrogenation catalyst at a temperature within the approximate range from 650 to 850 F., pressure within the approximate range from to 2500 p.s.i.g. and liquid hourly space velocity within the approximate range from 0.25 to 5; the severity of the second-named contacting being greater than that of the first-named contacting.

2. Process according to claim 1 wherein the oil is subsequently contacted with hydrogen and a metallic hydrogenation catalyst at a temperature within the approximate range from 600 F. to 650 F.

References Cited in the file of this patent UNITED STATES PATENTS 1,908,286 Dorrer May 9, 1933 1,934,063 Halsam Nov. 7, 1933 2,365,751 Drennan Dec. 26, 1944 2,376,086 Reid May 15, 1945 2,423,176 Cole July 1, 1947 2,459,465 Smith Jan. 18, 1949 2,779,713 Cole et al. Jan. 29, 1957 

1. PROCESS FOR PRODUCING STABLE PETROLEUM LUBRICATING OIL WHICH COMPRISES: CONTACTING PETROLEUM LUBRICATING OIL WITH HYDROGEN AND A METTALIC HYDROGENATION CATALYST A TEMPERATURE WITHIN THE APPROXIMATE RANGE FROM 450 TO 750*F., PRESSURE WITHIN THE APPROXIMATE RANGE FROM 150 TO 3000 P.S.I.G., ANS LIQUID HOURLY VELOCITY WITHIN THE APPROXIMATE RANGE FROM 0.5 TO 10; AND SUBSEQUENTLY CONTACTING SAID OIL WITH HYDROGEN AND A METALLIC HYDROGENATION CATALYST AT A TEMPERATURE WITHIN THE APPROXIMATE RANGE FROM 650 TO 850*F., PRESSURE WITHIN THE APPROXIMATE RANGE FROM 100 TO 2500 P.S.I.G. AND LIQUID HOURLY SPACE VELOCITY WITHIN THE APPROXIMATE RANGE FROM 0.25 TO 5; THE SEVERITY OF THE SECOND-NAMED CONTACTING BEING GREATER THAN THAT OF THE FIRST-NAMED CONTACTING. 